1. Field of the Invention
The present invention relates to a bubble jet head arranged in opposition to a printing surface of a printing medium for ejecting an ink toward the printing surface by a pressure of a bubble, and an bubble jet apparatus employing such bubble jet head.
2. Description of the Related Art
In a bubble jet head, there are an edge shooter type and a side shooter type, in general. In the edge shooter type bubble jet head, ink ejection openings are provided on an edge portion as downstream portion with respect to heater portions as ink heating portions provided for respective of a plurality of branched ink passages for delivering an ink from an ink storage portion. On the other hand, in the side shooter type bubble jet head, the ink ejection openings are provided in opposition to the heater portions provided for respective of a plurality of the branched ink passages.
In the side shooter type bubble jet head, high work efficiency of an electrical energy to be supplied to the heater portion is achieved for relatively short distance between the ejection opening forming surface and heating surfaces of the heater portions. On the other hand, the side shooter type bubble jet head is advantageous in that even when it is left for a while without being actuated and then printing operation is resumed in such condition, possibility of ejection failure incapable of ejecting ink droplet for increased viscosity of the ink due to evaporation of volatile component contained in the ink, can be significantly reduced.
In the side shooter type bubble jet head, as disclosed in Japanese Patent Application Laid-open No. 152068/1989, for example, there has been proposed one, in which the heater portion is disposed within a receptacle portion, one end of which is opened to an ink supply passage, and surrounded in order to reduce vibration of meniscus upon ejection of the ink and not to interfere ejection of the ink droplet, and a narrow passage portion (in the publication, it is referred to as "local restricting portion") is provided between a portion in the vicinity of an opening portion of a common ink supply passage and ends of respective ink supply passages.
On the other hand, as shown in Japanese Patent Application Laid-open No. 16365/1993, for example, there has been proposed one, in which bubble in expanded condition as heated by a heating surface of the heater portion is communicated with atmosphere in the vicinity of the ink ejection opening, and the ink covering the bubble and the ink in the vicinity of the ink ejection opening are continuous without being blocked by the bubble, so as to be employed in the side shooter type bubble jet head to efficiently eject relatively small ink droplet without spraying.
In such bubble jet head, for speeding up the printing operation, it becomes important to shorten a period for refilling of ink, as important factor for setting a driving frequency.
However, as in the foregoing example, when the heater portion is arranged within the receptacle portion and surrounded therein, and the descending cross sectional area passage portion (narrow passage portion) is provided between the opening portion of the common ink supply passage and the ends of respective ink supply passages, it is possible to increase flow resistance due to presence of the narrow passage portion. Thus, limitation should be caused in shortening of refilling period of the ink. On the other hand, upon high speed printing, residual bubble in the ink which should cause adverse effect of ejection speed of the ink droplet and ejecting direction of the ink droplet, can be retained within the ink supply passage due to presence of the narrow passage portion.
On the other hand, as noted above, when the bubble in the expanded condition as heated by the heating surface of the heater portion is communicated to the atmosphere in the vicinity of the ink ejection opening, and the ink covering the bubble and the ink in the vicinity of the ink ejection opening are continuous without being blocked by the bubble, since meniscus which becomes relatively large (after ejection of ink droplet (after cutting the ink droplet)) is caused, it becomes particularly necessary to reduce flow resistance. Therefore, influence of the narrow passage portion for the refilling period of the ink is significant.